Processes in which products are treated with ultraviolet light (UV) to effect polymerization, sterilization, etc., and in particular, the use of ultraviolet light for the curing of coatings, inks and similar materials, are becoming of increasing interest. Equipment designed for such processes is variously called a UV processor, UV drying oven, or other similar terms, but in general comprises one and usually several ultraviolet light lamps positioned so as to direct UV radiation onto a workpiece passed beneath the lamps, usually on a moving conveyor or web.
More recently, designs of such equipment have included various features to overcome problems encountered during utilization of the equipment in various types of processes. These features may include, for example, provision for maintaining an inert atmosphere within the UV processor, certain specialized reflector designs, shutters for blocking, as desired, some or all of the ultraviolet light from reaching the workpiece, and cooling means associated with the reflectors and shutters to remove some of the heat generated by the ultraviolet lamps. U.S. Pat. Nos. 3,733,709; 3,745,307; 3,769,517; 3,790,801; and 3,826,014 describe examples of such equipment.
As indicated, considerable heat is generated by the ultraviolet lamps and heretofore part of such heat has been removed by air or water cooling of the reflectors, shutters or other component parts of the UV processor. Usually it is not believed necessary to cool the workpiece itself, since heat often aids in effecting the desired polymerization, sterilization, or the like. It has been found, however, in some cases, and particularly where the product being treated comprises a material which can be adversely affected by prolonged heating, that it is desirable to control the surface temperature of the workpiece and to remove the heat from the workpiece as soon as possible following the treatment with UV radiation thereby preventing excessive buildup of the heat in the workpiece while it is passing under a plurality of UV lamps. Moreover, it is in such cases particularly desirable to provide for removing heat from the surface of the workpiece which is exposed to the ultraviolet radiation because this helps to prevent the heat from penetrating the workpiece. Cooling of the workpiece by cooling the conveyor or web, for example, does not achieve this result.
One instance where heat penetration and buildup is a problem is in the application of thin coatings to wood substrates, where it is desirable to remove the heat from the surface portion of the coated substrate before the heat penetrates and builds up in the wood substrate. Because wood and similar materials do not lose heat rapidly, if such builup occurs the heat is retained for unduly long periods thereby resulting in possible deterioration of the substrate and/or the coating thereon. Heat buildup is also a problem with coatings on thin metal substrates, which may flex due to expansion before the coating is fully cured, and with plastic substrates which may deform due to excessive heat.
While it is desirable to remove some of the heat generated by the ultraviolet lamp, it is usually not desirable to permit currents of cooling air to contact the lamp surface itself, because differential cooling of the bulb surface results with attendant deterioration and premature failure of the lamp. Thus, the cooling should be localized, insofar as possible, at the surface of the workpiece.
It has been suggested heretofore to utilize high-velocity air to cool a product being treated with ultraviolet light. The apparatus described for such purpose utilizes large volumes of air which then pass over and around the product, without provision for localizing the cooling by directing the inlet air and exhaust in the manner necessary, as described herein.